Apparatus for and method of producing metal tubes



May 8, 1934.

R. c. STIEFEL 5 FOR AN UCI Filed July 27, 1932 2 Sheets-Sheet l NNNNNN OR NG METAL TUBE May 8, 1934.

APPARATUS FOR AND METHOD OF PRODUCING METAL TI fBES Filed July 27, 1952 2 Sheets-Sheet 2 y' K i m. I

R. c. sTlEFEL. I 1,957,916-

?tent May 8, 1934 iTED STATES PATENT OFFICE APPARATUS FOR AND METHOD OF rnonUo- ING METAL TUBES I The invention relates to and is utilizable in the manufacture of metallic tubing in general, but is more particularly concerned with the manufacture of seamless tubing. It consists in a new method of forming such seamless tubing from a solid blank in the form of a round bar or billet, or from a hollow or partially pierced cylindrical blank, or for the further reduction and elongation of previously formed tubing, in all of which cases w the metallic piece being. subjected to the operation is herein termed inclusively the blank. Said new method also involves and requires the rolling, reduction andelongation of the blank in a mill of the well-known type wherein the it blank is subjected to the operation of a plurality of cross-rolls over and upon an internally arranged mandrel.

It is well known that cross-rolling a billet or ,metal blank on a mandrel tends to enlarge or expand the blank laterally, or circumferentlally of the mandrel, and that such expansion or lateral flow of metal greatly retards andinterferes withthe desired elongation of the blank. One of the objects of this invention is to minimize the so-called lateral flow of the metal, and to promote with better results the flow of metal more nearly along lines parallel to the axis of tube generation. Within practical limits I aim at maximum elongation of the blank per unit of wall reduction.

It is to be understood that by the term "crossrolls in the following specification and claims, I include disk rolls and other such rolls which in acting upon a billet tend to produce both rotation and the axial feeding. of the billet metal. I The invention will be'understood by a description of the operation of the apparatus illustrated in the accompanying drawings, which apparatus also constitutes a part'of the invention. Fig. 1 is a fragmentary view in plan of a mandrel, upon which a billet is positioned and subjected to' a set .of section being denoted by-theline IIII in Fig.

1. Fig. 3 is a view of the mandrel in side elevation, and shows, partly in vertical section and partly in side elevation, a billet upon the mandrel being operated upon by the cross-rolls. Figs. 4 and 5 are vector diagrams. Fig. 6 is a fragmentary view, similar to Fig. 3, illustrating the practice of the invention in the manufacture of seamless tubing directly from a solid billet. Fig. 7 is a view similar to Fig. 6, illustrating a mandrel of modifled structur'ea floating mandrel which also admits of the practice and advantages of the invention. And Figs. 8 and 9' are views corresponding generally to Figs. 1 and 2, showing the practice of the invention with still another organization of cross-rolls.- g

7 Referring to Figs. 1 to 3 of the drawings, I have 3 shown in exemplary 'waya mandrel 1 whose working tip or nose 2 is located centrally between three cross-rolls 3, 4, 5. The general shape of the rolls is well-known, and their specific form and size are readily determinable by the engineer. In this case I show the three rolls to be of the same dialneter and equispaced (120 apart) about the mandrel, see Fig. 2. The mandrel I is secured against axial movement, while being free for rotation, in a suitable support which is located to the right at an interval from the rolls in Fig. 3. According to usual practice the rolls 3, 4, 5 are adjustably journaled in'a machine bed and frame, and means are provided for powerfully rotating the rolls, as indicated by the arrows in the drawings. The mandrelsupport and the machine bed are not shown in the drawings. their provision'being also a matter of known engineering practice.

A pierced billet, or a hollow cylindrical blank of metal, B; is shown inplace upon the mandrel, and the rolling down process and the formation of a tube T is illustrated in Fig. 3. As mentioned above, the three cross-rolls 3, 4, 5 are of one size and are equispaced with respect to the mandrel,

and thus the pass line, denoted m:::, of the metal of the group of rolls is known as the normal pass line, but it must be understood that the characteristics of metal flow in general and the advantages of the invention in particular, which I describe'belg can be obtained in cases where the pass line is oilset from the normal, or where the rolls are of unequal diameters, and also in cases where the rolls exert unequal forces upon the metal being worked.

For a better understanding of the invention, 1 will first consider the behavior of'the metal 1% under the action of the cross-rolls. Of course. the cross-rolls 3, 4, 5, in rotating about axes that are disposed. angular-1y to the blank upon man drel 1, have each a linear velocity component extending parallel to the pass line :vz, and a 1 rotary velocity. component tending to produce rotation of the blank and the mandrel upon which it is positioned. The diagram in Fig. 4 illustrates the relation stated: the dotted line a:--a: represents the pass line, the dotted line 116 y-y denotes the axis of one cross-roll, and the vector A-C denotes the tangential or resultant velocity of the roll at the central point of contact with the billet. The resultant velocity (AC) comprises two components, one component A-B indicating graphically the linear velocity, the velocity value tending to produce linear movement of metal along the mandrel, and the other component AD indicating the rotary velocity, the velocity value tending to produce rotation of the blank and mandrel. Assuming that there be neither reduction in wall thickness nor elongation of the blank, the above defined velocity components would indicate accurately the movement of metal; it would manifestly be a pure helical advance of the blank over the mandrel. However, the considerations are more involved. The cross-rolls in drawing and forcing the blank over the mandrel exert a continuous compressive action upon the metal of the blank, and this action produces a flow of the metal which effects the desired wall reduction of the blank. The desideratum is .to confine substantially all metal flow along the extent of the mandrel, that is, to employ all .iiowed metal in effecting tube elongation. However, the metal tends to ilow in two directions. In addition to the desired flow longitudinally of the mandrel, there is a flow circumferentially of the mandrel, tending to increase the diameter of the tube in the manner indicated by the dotted lines E in Fig. 2. When it is desired to obtain large reduction of wall thickness or great elongation of the blank, the consequent tendency of the blank to increase in diameter may result in very pronounced lateral distortion, and cause the blank to stick between the rolls.

The tendency for metal flow is governed by what is technically known as the flow angle. In Fig. 2 the flow angle b, between the mandrel face and the face of roll 5, is the factor determining circumferential or tube-expanding flow at E, while the flow angle a, Fig. 3, is the factor upon which depends the linear flow of metal along the mandrel. In regulating these flow angles, by the adjustment and design of the rolls and mandrel, the flow of metal can within certain limits be controlled. In order to efiect tube elongation in relatively large measure, it will be manifest that the fiowangle i) should be as small as is practically possible, and that the angle a should be as large as possible in relation thereto. However, inasmuch as the blank, under the action of the rolls, is comparatively free to rotate with the mandrel, but is subject to frictional resistance in linear flow on the mandrel, it will be evident that the resistance is greater to metal flow in the longitudinal direction than in the transverse or circumferential direction. I have found that the linear flow angle a, Fig. 3, cannot be increased to such value as to overcome the effect of this frictional resistance and to produce the desired longi tudinal flow of metal. Ihat is to say, I have found that if the flow angle a is increased to such degree as might produce the otherwise desired results mentioned, it (the angle a) becomes so great or abrupt as to prevent the blank from entering and moving between the mandrel and cross-rolls. My invention lies in the discovery of how this objectionable condition may be effectively overcome, and in overcoming the objection I am able to obtain maximum tube elongation per unit of wall reduction. Accordingly, fewer passes are required to convert a blank into a finished seamless tube, less time is required for the manufacturing process, and there is an accompanying conservation of heat in the blank.

In brief, the invention includes the exertion of tension longitudinally upon the metal flowing between the rolls and the mandrel, and this tension is in part obtained by an adjustment of one or more of the cross-rolls. In Figs. 1 to 3, the roll 3 is the tension roll. In Fig. 4 the angle 0 represents the effective angle between the pass line .r--a: and the axes of rolls 4 and 5. Rolls 4 and 5 are both driven at an R. P. M. which gives the faces of the rolls a tangential or resultant velocity of AC feet per minute. The resultant velocity AC, as hereinbefore stated, has two components; the component AD representing the velocity in feet per minute of the faces of the rolls 4, 5 tending to produce rotation of the blank, and the component A--B representing the velocity of the rolls tending to produce movement of the blank longitudinally of the mandrel or pass line.

The third roll, 3, is adjusted at such an'angle d to the pass line 17-12, and is rotated at such resultant or tangential speed EG, that its velocity component E-H (Fig. 5) equals the rotary velocity component A-D of rolls 4, 5, while the linear velocity component E-F exceeds that (A-B') of the rolls 4, 5. Accordingly, the velocity component AD of rolls 4, 5, in being equal to the velocity component E-H of roll 3, produces precise harmony among all rolls in their tendency to produce rotation of the blank, while the linear velocity component EE of roll 3, in being greater than the velocity component AB of rolls 4, 5, produces a pull on the metal of the blank in the direction of tube elongation. So the operation of the cross-rolls is controlled in such manner that at least one of them has a greater linear velocity component than the others, and thus the metal of the blank in moving over the mandrel is placed under tensionso as to aid the longitudinal flow angle a (Fig. 3) in promoting elongation of the tube rather than its cross-sectional expansion; and by keeping the rotary velocity components of the rolls equal, the tendency toward lateral distortion of the tube being rolled is substantially reduced or eliminated.

It will be understood that the invention can be practiced in the well-known arrangement of two opposed cross-rolls in combination with intermediate and opposed stationary guides. That is, the cross-roll 6 in Fig. 6 can be operated with a greater linear velocity component than the roll '7, and the desired good results can be thereby obtained. Fig. 6 also illustrates that the method is applicable to billet-piercing millsmills in which solid billets (10) are formed into tubes. Fig. 7 illustrates a still diiferent mill, a mill in which the mandrel 8 is free to move axially as well as to rotate with the blank or billet 9. In this case the cross-roll 11 is, in the manner explained, caused to exert tension upon the metal flowing between the mandrel and rolls.

Figs. 8 and 9 show a set of cross-rolls comprising two co-operating pairs of cross-rolls, 12, 12 and 13, 13. In this case also the mandrel 14 is shown for convenience to be on the normal pass line of the set of cross-rolls. It will be perceived that the rolls 12, 12 are larger than the rolls 13, 13. As a matterof choice the smaller rolls are arranged with greater obliquity to the pass line than the larger rolls, and the smaller rolls are so rotated as to have the greater linear velocity component and. to exert the described tenits sion upon the metal of the blank 15. In general, I do not confine my invention to any particular arrangement of cross-rolls, and I contemplate practicing the method of the following claims in any machine wherein two or more cross-rolls cooperate for the working of metal blanks.

It is particularly to be noted that the results and advantages described are obtained in a single pass of cross-rolls. In moving through the single pass the metal of the blank is progressively subjected to tension, and such tension is progressively effective over the entire length of the blank. Accordingly, the tube is subjected to metal-working conditions that are uniform throughout its length, and .the resulting product is correspondingly more uniform in physical characteristics. These are advantages which manifestly cannot be obtained in a method in which the blank is fed through two or more successive passes, and the rolls of the second pass caused to exert tension on the metal leaving the first pass.

It may further be remarked that all rolls in .the pass are metal-reducing rolls, and that no while the longitudinal velocity component (A-B,

Fig. 4) is referred to as linear velocity.

While the various forms of apparatus herein shown and described have a common feature, of

substantial novelty includedwithin the scope of the invention, it will be understood that the described method of manufacture may be practiced by the use of apparatus of other and different plurality of cross-rolls, at least one of the rolls having its obliquity with respect to the pass line,

and its speed, in such relation to the other roll or rolls that its linear velocity is greater than, while its blank-rotating velocity substantially equals, 7

that of the other roll or rolls.

2. In reducing and elongating a tube by subjecting a blank upon amandrel to the action of -a pass of cross-rolls, the method of applying tension upon the blank in said pass which comprises ro tatin'g each of said-rolls upon an axisinclined to the axis of said mandrel, and, by determining the axial inclinations and relative angular velocities.

of said rolls; producing in'at least one of said cross-rolls of the pass a blank-feeding velocity which is unequal to such velocities of the remain ingrolls of the pass, while causing all cross-rolls of said pass to rotate with substantially equal blank-rotating velocities.

3. In drawing a blank over a mandrel, by the action of apass of cross-rolls, for the production of a seamless tube, the herein described-method which comprises rotating the cross-rolls of said pass with substantially equal blank-rotating velocities and unequal blank-feeding velocities, and, by means of the resultant differential feeding action of the rolls of said pass, subjecting the metal to tension.

' RALPH C.STJEFEL. 

